Acne Keloidalis Nuchae 

Acne keloidalis nuchae (AKN) is a scarring form of chronic folliculitis that manifests as follicular-based papules and pustules, which eventuates in keloidlike lesions. The lesions are most pronounced on the occipital scalp and the posterior part of the neck, and they occur almost exclusively in young males of African descent.^[1] The term acne keloidalis nuchae is somewhat of a misnomer because the lesions do not occur as a result of acne vulgaris and are histologically not keloidal.^[2]

Acne keloidalis nuchae was first recognized as a discrete entity in the late 1800s. Hebra was the first to describe and document this condition in 1860, under the name sycosis framboesiformis. Subsequently in 1869, Kaposi described this same condition as dermatitis papillaris capillitii.^[3] The term acne keloidalis was then given to this condition in 1872 by Bazin, and, since that time, this is the name most often used in the literature.^[2]

Clinically, the lesions initially manifest as mildly pruritic follicular-based papules and pustules on the nape of the neck. Because the folliculitis is persistent, ultimately keloidlike plaques eventuate. The area is typically hairless, but broken hair shafts, tufted hairs, and ingrown hairs can sometimes be identified within and at the margins of the plaques. Over time, the plaques typically slowly expand. The lesions are disfiguring and can be painful. Abscesses and sinus tracts with purulent discharge may develop in advanced cases. Comedones are not a common feature of acne keloidalis nuchae.

The exact etiology of acne keloidalis nuchae (AKN) remains obscure; however, one postulation is that chronic irritation and inward growth of coarse, curved hairs may play a role in the development of these lesions. This hypothesis is supported by the fact that lesions are exacerbated by close shaving and/or recurrent rubbing of the area by clothes or athletic gear. In a study of 453 high school, college, and professional American football players, 13.6% of African American athletes had acne keloidalis nuchae, whereas none of the white athletes had acne keloidalis nuchae.^[4]

Similar to pseudofolliculitis barbae, a condition that also occurs more commonly in African Americans, some have proposed that close shaving or shearing of coarse, curved hairs facilitates the reentry of the free end of the hair into the skin, which then invokes an acute inflammatory response. Men who have haircuts more frequently than once a month are at higher risk of developing acne keloidalis nuchae.^[5]

Although the ingrowing hairs account for small papules, they are not sufficient to explain the progressive scarring alopecia that occurs in some patients. Patients with progressive scarring alopecia often exhibit recurrent crops of small pustules and may have a condition akin to folliculitis decalvans. Chronic low-grade bacterial infection, autoimmunity, and some types of medication (eg, cyclosporine, diphenylhydantoin, carbamazepine) have also been implicated in the pathogenesis in some patients.^{[6, 7]}

Sperling et al classify acne keloidalis nuchae as a primary form of inflammatory scarring alopecia and suggest that overgrowth of microorganisms does not play an essential role in the pathogenesis of acne keloidalis nuchae. They also found no association between pseudofolliculitis barbae and acne keloidalis nuchae.^[8]

After extensive histological and ultrastructural studies of acne keloidalis nuchae lesions, Herzberg et al proposed that a series of events must happen in order for acne keloidalis nuchae to occur, namely the following^[9] :

1. The initial process begins as acute perifollicular inflammation followed by weakening of the follicular wall at the level of the lower infundibulum, the isthmus, or both.
2. The naked hair shaft is then released into the surrounding dermis, which acts as a foreign body and incites further acute and chronic granulomatous inflammation. This process is clinically manifested by small follicular-based papules and pustules.
3. Subsequently, fibroblasts deposit new collagen and fibrosis ensues.
4. Distortion and occlusion of the follicular lumen by the fibrosis results in retention of the hair shaft in the inferior aspect of the follicle, thereby perpetuating the granulomatous inflammation and scarring. This stage is marked by plaques of hypertropic scar.

Frequency

United States

Acne keloidalis nuchae is said to represent 0.45% of all dermatoses affecting black persons.

Mortality/Morbidity

The plaques of acne keloidalis nuchae slowly expand over time, and, although medically benign, acne keloidalis nuchae can be a psychologically devastating condition. Chronic pruritus and drainage may occur, and, ultimately, scarring alopecia may ensue.

Race

Acne keloidalis nuchae is most prevalent in African Americans; however, it has occasionally been reported in Hispanics and Asians, and, rarely, in whites.

Sex

Although early literature inferred that acne keloidalis nuchae only affects males, it is now known to occur in females, with a male-to-female ratio of approximately 20:1.^[10]

Age

Most cases occur in persons aged 14-25 years. Lesions manifesting prior to puberty or in persons older than 50 years is unusual.^[8]